Up to now, a fluid pressure cylinder employed in a clamp device or the like that clamps an object to be clamped, such as a workpiece etc. that is to be subjected to machining, has a main cylinder body, a piston member that is provided so as to move forwards and backwards freely within the main cylinder body, a fluid pressure operation chamber for driving the piston member toward at least one of the advance side and the retraction side.
Now, various types of rod position detection technique have been implemented in practice for detecting the forward limiting position, the rearward limiting position, an intermediate position of the piston member of the fluid pressure cylinder.
For example, the clamp device of Patent Document #1 detects the position of a piston rod with a pressure sensor that detects a fluid pressure supplied to a fluid pressure cylinder, and two position sensors that, detect a raised position and a lowered position of a detected element on the lower end portion of an actuation rod that is projected downward from a piston member of the fluid pressure cylinder to the exterior.
And, in the clamp device of Patent Document #2, a mechanism that operates together with the raising and lowering operation of an output rod of a fluid pressure cylinder to open and close an air passage is provided at the exterior of one end of the main cylinder body, and thereby this structure is capable of detecting the raised position and the lowered position of the output rod.
Moreover, with the clamp device of Patent Document #3, a workpiece holding stand that supports and holds the object to be clamped is provided independently. The workpiece holding stand includes a pad member in which an air ejection outlet is formed and an external barrel member that supports the pad member while elastically biasing it toward the object to be clamped. When the pad member is in its projected position, pressurized air is ejected from the air ejection outlet, and when the clamp device is driven for clamping and the pad member is pressed and retracted by the object to be clamped, the air ejection outlet is blocked by the outer barrel member, so that the pressure of the pressurized air rises and the fact that the clamp device has gone into its clamped state can be detected.
Patent Document #1: JP Laid Open Patent Publication 2001-87991.
Patent Document #2: JP Laid Open Patent Publication 2003-305626.
Patent Document #3: JP Laid Open Patent Publication 2009-125821.